1. Field of the Invention
This invention relates to a method of reading the data contents of an optical fiber line.
2. Description of the Related Art
Digital circuits used in the computing, networking, and communications industries have steadily moved towards higher speed, channel capacity, and reliability. The costs of piece parts, functional assemblies, system blocks, networks, and the services sold to end-users are simultaneously plummeting. Customers demand transparent access to faster networks with commensurate improvement in service offerings and uptime.
The standard practice in wide-bandwidth communication networks is to convert electrical impulses into light pulses and to propagate these pulses through optical fibers to their destinations where they are converted back into electrical signals. This eliminates a number of fundamental bottlenecks inherent to directly sending an equivalent amount of information in the same amount of time by purely electrical means. Technological developments in optical fiber materials, laser sources, detectors, and networks have proceeded at a pace faster than that of semiconductor electronics.
Optical diagnostic and switching methods, however, have not kept pace and are the primary roadblocks to growth in this sector. Electrical signals propagate as pulses along circuit traces and wires. They generate electrical fields which can be probed often without significant degradation of the pulse energy. However, most often the readout is destructive with a consequent storage of the pulse bit stream into a shift register and consequent regeneration of the bit stream in the original format. Optical pulses, on the other hand, are confined to propagating along the guiding structure of an optical fiber, and the energies in each pulse are small. Conventional ways of examining an optical data stream and making a decision based upon that result require destructively converting the optical pulses into electrical signals, using electrical methods to make the decision, regenerating the optical pulse train, and coupling it back into a specified optical fiber.
This is a complex, costly process with considerable scope for introducing, amplifying, and propagating errors. In addition to switching, examining an optical data stream for “signature analysis,” fault testing, housekeeping, and/or sampling, as is routinely done in the test-and-measurement of electronic digital circuitry, has not been accomplished by optical techniques. All of these functions are typically done by storing the data stream in electronic shift registers. Additionally, conventional methods for “tapping” an optical line require disclosing the existence of a tap.